Catalysts for conversion of hydrocarbons



CATALYSTS FOR CONVERSION OF HYDROCARBONS Robert P. Sieg, Berkeley,Calif., assignor to California Research Corporation, San Francisco,Calif., a corporation of Delaware I No 'Drawing.' Filed une as,1957,Ser. No."568,605 4 claims. or. 252-465 This invention relatesto thecatalytic conversion of hydrocarbons byv a cyclic, generally adiabaticprocess wherein the desired diolefin or other products are formed during.an endothermic dehydrogenation or conversion step which is followed byan exothermic regeneration step wherein carbonaceous deposits'formed onthe catalyst surface during the conversion portion of the cycle areburned therefrom, thus furnishing the catalyst bed with the heatrequired in the succeeding conversion step. The invention isparticularly directed to a novel catalyst which makes it possible topractice this operation at relatively .high temperatures with improvedselectivity and much longer totaloperating periods than has heretoforebeen possible.

This application is a continuation-in-part of co-pending applicationSerial No. 518,919, filed June 29, 1955, and now abandoned.

. In carrying out a cyclic, adiabatic operation of the type towhich-this invention relates, it is desired that there be as high aperpass conversion as possible, commensurate with good dehydrogenationselectivity. That is to say, there should be produced maximum amounts ofthe desired products per given amount of feed converted. Otherconditions remaining the same, an increase in average reactiontemperatures normally results in higher per pass conversions. Further,in the case of butadiene, at least, .an increase in, temperature effectsa shift towards butadiene of the butene/butadiene thermodynamic equilibrium. However, with the catalysts heretofore employed in commercialoperations it has not been possible to take advantage of thebenefits tobe gained by operating at relatively high temperatures over the fulllife of the catalyst. Such catalysts, which are made up of chromiumoxide deposited on an activated alumina of the Bayer Processtype,(i.e.', one prepared by precipitation of the alumina from analkaline aluminate solution such as an aqueous solution of sodiumaluminate) have good total conversions and dehydrogenation selectivityvalues when relatively fresh. However, as they'remain inservice forseveral months, dehydrogenation selectivity falls ofi? in an appreciablemeasure, as does the over-all per pass conversion.- While higherconversion levels can be obtained with such less active catalysts byresort to higher temperaturcs, this'leads to still more rapiddeactivation and even poorer. selectivity, as evidenced by afalling offin the relative .amountof butadiene or other desired product and byan-increase in the relative amount of coke laid down, on thecatalystduring the on-stream period. .,With increased coke lay-down,more heat is, in .turn, released during succeeding regeneration portionsof the operating cycle, thus giving rise to temperature run-awayconditions, with consequent deactivation of the catalyst.

It is a general object of the present invention to provide a hydrocarbonconversion process of the cyclic, adiabatic type wherein the catalystemployed is. capable of giving good performance from the conversion andselectivity I standpoints over a relatively long operating period beforecatalyst replacement is required.

2,943,067 -Patented June 1 96O ing the dehydrogenationof hydrocarbons,.particularlyof C to C branched and/ or straight chain hydrocarbons, ormixtures thereof. I g

The present invention is based on the discovery. that the foregoingobjects are attained by employing as the catalyst in the cyclic,adiabatic operation a particulate mass having a surface area less thanabout -l00. mfi/g. .and which is comprised of alumina of so-called gelorigin-on which'are deposited a total of from about 3 to,.40% of oneorjmore group VI metal oxides selected from the group consisting ofchromium oxides and molybdenum oxides, together with a total of fromabout 0.025 to.3.0% of one or more alkali metal oxides; selected fromthe group consisting ofpotassium oxide, lithiumoxide and rubidium oxide.An alumina-chromia-potassium oxide catalyst is preferred. When. used indehydrogenation conversion reactions leading to the production ofbutadiene, the amount of alkali metal oxidein the catalyst is maintainedbelow 0.5%, while the group VI metal oxide is preferably maintained in arange of from i to 25 The catalyst of the presentinvention canbe;employed in a .wide variety of operations, includingprocesses for thecracking, reforming -dehydrogenation and isomerization of hydrocarbons,However, it is particularly well adapted for use in'cyclic, adiabaticoperations involving the dehydrogenation of aliphatic hydrocarbonscontaining from 2 to 5 carbon atoms in'the molecule, Of suchdehydrogenation reactions, those resulting in the production of butenesfrom n-butane, and more particularly of butadiene from n-butane andn-butenes, are presentlyof the hereinafter asit relates to operationswherein butadiene is producedfrom abutane-rich feed stream, withadditionaL infor rnation also. being given as to theproductionof;isoprene from isopentene v lthoughfthe catalyst of the presentinvention canibe prepared 'by various methods, a preferred met od is,-.to proceed by the following sequence of steps; Q5

(1) The gel-type aluminasupport is impregnated with a predeterminedamount of an aqueous solution ofa potassium or other alkali metal salt,followingwhich the resulting material is dried and calcined attemperatures above 1400 F. to effect a significant reduction in thesurface area of the material, e.g., to a range-'ofifrorn about 2 Thecalcined, alkali oxide-containing alurninal is impregnated with anaqueous solution of a heat decotnposable salt of'chrominum ormolybdenum,;- following which. the, material is; again driedand,calcined at tern peratures above 1300" F :,to ,convertthesalt to theoxide and to bring the final surface area ofthe catalyst mo 1 V The p rd p op ratq y m th d r e tedoabove 4 will now be described in'greaterdetail.,. The gel-type alumina base can be prepared, forexample,-;;by,precipie tation from an acidic, aqueous solution ofvaluminum spl-v fate, nitrate or vother salt, by the .additionofarnmoniumhydroxide or,v other alkaline precipitating agent. The. re-

sulting hydrogel is thereafter washed and filtered. to remove soluble,inorganic contaminants. Thewashed product is dried, preferably by spraydrying methodsto secure. afinely divided powder. The powdered irnaterialis then..slurried with. a. solution of a heat-decomposable salt of thealkali metal (preferably potassium carbonate, bicarbonate or hydroxide)or an alkali metal salt of an anion 'of the group VI metal, e.'g.,potassium 'chromate, in.a..concentration suflicient to yield a finishedcatalyst 'of. desired alkali'metal content. The resulting slurry isdried (e.g., six hours at 350 F.), mixed with graphite or otherpelleting lubricant, and then pelleted. The pel- 'lets..are. thencalcined at temperaures above about, 1400" F. to .gonvert the alkalicompounds employed to the .oxide form, to .removevolatile impurities andwater of hydration,.'and to. decompose any lubricant employed. Atthe'same time, the calcining treatment, which in many .cases is.conducted for from 3 to 7 hours at 1700-1800 F for example, effects asubstantial reduction in the surface. area of. the catalyst. This areais normally in excess. of 200 'm. /g. in the case of the gel-typealumina starting material, and is normally reduced to a valuebetweenabout 80 to 150 mP/g. as a result of the calciniugfollowi'ng thealkali metal impregnation step. As indieated tlieltime and temperatureof this calcining'operation may bevaried within fairly wide limits withlonger times being required at correspondingly lower temperatures. Aminimum temperature consistent with reasonable. calcining times is about1400" F., while temperaturesabove about l900-2000 F. should be avoidedin so far as possible in order to prevent damage to the catalyststructure. If desired, steam may be substituted for dry air incalcining, the efiect of steam being to reduce calcining temperaturesand/or times. Thus, the 'samefinal area is attained for heat treatmentfor 26 hours at 1600 Ffin dry air as in 4 hours at this same temperaturein a steam atmosphere.

Instead of. employing the foregoing procedure in which thealuminagel'powder is slurried with an aqueous solution of alkali metalsalt, the alkali metal compound can be introduced by blending the drygel powder with a dry alkali metal salt. Alternatively, the gel-typealumina may be pelleted and precalcined until its surface area isbrought approximately within the aforesaid 80-150 mF/g. range, with thecalcined pellets then being impregnated "with a solutionof the alkalimetal salt. In the latter method, nocalcining'step need be practicedfollowing the alkali metal impregnation treatmentunless it is desired toeffect a further reduction in the surface 'area of the "product prior totreating the samewith the group VI metal compound. However, the firstmentioned slurry method is preferred, since itresults in a finishedcatalyst having-greater activity and better selectivity than thatprepared by dry mixing or 'by pellet impregnation.

1n the eventthat more than the desiredamount' of alkali metal o'x'ideisobtained in the catalyst, the excess may readilybe leached out with hotwater either before or after the-steps of addingthe groupVI metalcompound andcalcining thepro'duct. In this connection it should be:noted th'at substantially all ofthe potassium or other alkali metalemployed can be removed by such leaching process, since it exists in thecatalyst primarily inthe form of soluble sans rather, than "insoluble,Spinel-type co -puaas rormed ingmiaor mounts by reaction of the Ealkalinietal o'xidewith the alumina base when calcining temperatureswwewoonooo: are employed.

- 'l'ro'c'eeding'ito; step 2 6f the :preferred-preparatory meuio'd,"tliejealcihed alk'ali oxidecontaining catalyst is then impregnated withan aqueous solutionof the group VI "metal n1pen m-,"iarerb1 "a'chromiumcontaining, flieat' deeojmposable compc'iiind' such as chromicacid, "ehromiefnitrate,airinitiniuni'dichromate or the like. Thecatalyst is then carcassesive ofi volatile components ane to; deednaosetn chromium eor npound to the oxide, while also -'fur'ther reducingthe surface area .of .the catal-yst. -Suitable calcining "temperatureswill range from about 1300 toabout' l700 F;,the lo w en limitbeingeonisistent with-lfreas'onable calcining, times and :the upperlithitbe'irig' 's'et'byi'ea'son arise 'tndeac' br the curmium yield of68.6%.

4 oxide to sinter the catalyst at. highertemperatures... In any case,the controlling factor is to obtain a finished catalyst having a surfacearea of about 30 to 100 m. /g., while for operations leading to theproduction of butadiene, the surface area should preferably be betweenabout 50 and m. g. Such levels can be reached in many cases by calciningthe catalyst at temperatures of from about 16001 700 F. for periods of4-6hours, or even less, with somewhat longer periods being required atlower temperatures. The lower limit of 3.0 to 50 mP/ g. is set so as toinsure a catalyst having reasonably high activity, as evidenced by goodconversion of the reactant feed, while the upper limit of 80-100 m.?/g.is setsince catalysts of higher surface area than this tend to producedisproportionately large amounts of coke and thus must be operated attemperatures so low as to be uneconomic from the yield and conversionstandpoints, if temperature run-away is to be avoided. This is borneout. by the'data presented in Example II below, which show that inoperations leading to theproductio'n of butadiene, it is highlyadvisable to employ a catalyst having an initial surface area belowabout 80 m g. ifthe operation is to be conducted at eflicient hightemperature levels from the outset. Further, it has been found thatcatalysts having the. defined, relatively low surface area retaindesired performance characteristics for operating periods which are atleast as'long, and in some cases longer, than those which are broughton-stream at unduly high surface areas.

In referring herein to surface area, it is contemplated that the same bedetermined by conventional nitrogen adsorption methods.

The foregoing two-stage procedure for area reduction and metalsimpregnation of the aluminagel base is preferred to an alternateprocedure using simultaneous metals impregnation and single-stage heattreatment, in

per. pounds of feed passed throughthe catalyst in thereaction zone; inother words, the weight of butane in l00pounds of feed, minus the weightof butane inthe product from 100 pounds of feed. Butene conversion"refers to the pounds of butene destroyed per 100 pounds of feed, itbeing assumed that allbutane destroyed is first converted to butene, andthat the latter is converted in part to butadiene, hydrogen, coke,andpropene and lighter. Thu s, bu tene conversion is pounds butene in100 pounds feed plus butane converted per 100 pounds feed minus poundsbutene in product from 100 pounds feed. Total conversion is the sum ofthe respective butane and butene conversion figures. The termdehydrogenation selectivity," as employed herein, is a funcrecycled tothe conversion zone) can be converted to butadiene in a separatedehydrogenation 'process in a Specifically:

Dehy drogenation selectivity= 100 Butane conversion The numerator of thefraction in,th e above equation is defined as the butadiene equivalentyield.

5 EXAMPLE 1 i This example is presented to show a comparison between theactivity levels of a Bayer Process alumina catalyst and of gel-typealumina-supported catalysts conlet temperature as used for thehydrocarbon feed)1to burn ofi carbon deposits and effect someleveling'of bed temperatures; and 10' minutes intermediate time forpurging with nitrogen'and for evacuation between the g various amountsof alkali metal component An make and regeneration steps of the cycle. 1catalysts contained Cr O in quantities as indicated in In this 'type ireactor.s.ystem the catalyst bed must Table I below. The catalyst usedin runs 2663, 2665 always operate m i fl ovarian zero net heat; and 2675was a commercial burtadiene catalyst of the h the enflothemuc riaaotlonheat of dehydmgqna- Bayer type (Harshalw Chemical Company) while thetion, exothermic regeneration heat of coke combustion, maining catalystsshown in the table were prepared from and other sources of mput or isuch'as a geHype alumina catalyst (Fiurol Alumina N0 90 bleheat of feedand air, must total zero m order to con- 9 product of the FiltrolCorporation), by the two-stage, tmually. reproduce same memliemtures andslurry method described above Results are given both convers ons cycleafter cycle. Smce reaction and coke as to fresh catalyst, as well asthat given an accelerated r q i do q necessanly occur m exactly the 1aging treatment at 1600' F. to simulate commercial p m an poimons thecatalyst d some usage. In this connection, it has been found that treatWm tend be m.negatlve heat W cool whlle ment of the finished catalyst at1600 F. for periods of other pomons W111 fi posmve heat and 4, 24 and 64hours has approximately the same efiect on 13:2 ti g i g gg g my gwezl55?" the catalyst (as determined by surfiace area and by over- 6 Beregqner on gases a s e e all performance characteristics) as does actualplant temperauire profile attalped Much negative net usage for periodsof 3, 6 and 9 months, respectively. i gj fi gi gg ggi i f t m i fi z Thedehydrogenation runs shown in Table I were con- 1 d b 6 pos we me g'ducted in a pilot, adiabatic unit with semi-automatic concoo g i an m ii ifi or t e trol in order to reproduce commercial operating condieaexcess; 8 e an I {generation at i g tions. The feed employed was 98%butane. The unit turesare t eteafiar gradual y increased to m isoperated on a minute cycle: 10 minutes hydrocarmum P for g'lven feed andhydrocarbon bon feed at 1.45 v./v./hr., 6 inches of Hg absolutepresfeefl composltlon, P011111 W111 1 1 5! f at sure and the indicatedinlet temperature; 10 minutes air which runaway temperature condltlonW111 Obtam r feed at about atmospheric pressure (and at the same intheoutlet of the I6 the System will be 1101011891 f Table l Catalyst TypeCommercial Bayer Precipitated Gel Run N0 2663 2665 2676 2761 2771 26942713 2760 2770 2706 Composition:

K10, Wt., Percent 0 0 0 0.04 0 04 0 10 0.10 0.10 060., Wt., Percent 18.618.6 18.6 21 26 21 25 17.27 17 27 19 6 19.6 16.67 Added Heat Treatmentat 1,600 F., Hrs 4 28 26 26 26 'Iem erature, F 1600' 1600 1600 1600 1600Surface res, m 37 19 67.3 32.6 64 64.6 66.4 40.9 78.1 1 1 /161 'r z gag1,100 1,126 1,140 1,035 1,080 1,076 1,176 1,100' 1,130 1,106 to 11C 8S15 61138112 coke flf j 1.6 1.4 1.1 1.7 1.4 2.6 2.5 1.6 1.5 2.5Hydrogen. 2.2 2.0 1.4 1.0 1.0 2.4- 2.2 1.1 1.2 2.3 C; plus C; 7. 6 6. 06. 8 2. 6 2. 9 4. 7 5.3 a. 2 4. 9 6. 4 Butadiene 8.0 7.2 4.4 -6.2 6.36.7 8.0 6.9 9.6 6.6 Butenesa1. 2 24. 8 11.6 24. 1 2a. 6 2s. 1 26. 1 27.6 25. 0 27.7 Butane 61. 0 58.4 74. 8 66. 6 64. 6 66. 6 67. 0 69. 6 67. 866. 5

Butane Conversion, Percent 47.0 39. 6 23.2 32. 5 33. 5 42. 5 41.0 38.440. 2 .42. 5 Butane Conversion, Percent 15.8 14.8 11.7 8.4 9.9 14.4 15.910.8 15.2 14.8

Total Conversion, Percent; 62. 8 54. 4 34.9 40. 9 43.4 56.9 56. 9 49.255. 4 67. 3

e an iv y Coke/Dehydrogenation Radio 3. 4 3. 6 6. 4 4. 9 3. 9 6.0 6.1 3.9 3. 4 6. 1

Catalyst Type Precipitated Gel Run NO 2717 2721 2737 2716 2735 2716 272aGEL-128 CRL-128 Composition:

.26 66 66 .2- .2- 29-58 2133 .17 61 T2 3 ercen 1 Added Hat Treatment8.1; 1,600 F., 1311's.--- 26 26 24 24 26 Temperature, F 1600' 1600 16001600 1, 600 Surface Area, rim m. 41.0 67.0 42.3 48.9 36.2 61.5 46.8 70.355.3 l gta 11 1 6 T em rs nn 1,146 1,120 1,146 1,160 1,146 1,086 1,070980 1,016

10 116 113 SIS, 9106111 Ookeuuj 1.7 1.9 1.7 2.3 2.2 1.2 2.4 0.6 Hy ogen2.4 2.6 1.4 2.6 1.0 1.6 1.6 0.1 01 plus 0 5.3 4. 6 I 6.2 6. 5 5.2 3.6 4.6 3.1 Butadiene 9. 9 7. 8 9. 2 9. 8 7. 6 5.1 5. 2 1. 1 Butenes 24.2 26.422. 4 21. 3 14. 7 17. 2 11. 3 1. 7 Butane 66.4 66.8 Y 60.0 67.7 69.271.2 74.9 93.3

Butane Conversion, Percent- 41. 6 41.2 38.0 40.3 28.8 26.8 23.1 4. 7Butene Conversion, Percent 17.4 14. 8 15. 6 19.0 14.1 9. 6 11.8 3.0

Total Conversion, Percent 59.0 v 56.0 53.6 59.3 42.9 36.4 .349 7.7gutagienze Equivalent Yield g g (7i Z 1) (1) 43.3 6 e0 1V1 y 1Coke/Dehydrogenation Radio I 3. 9 '4. 5 4. 2 5. 6 7. 3 11.2 15. 3

1 wtcokexioo 2(Wt. ButadieneH-wt. butene undercontrol. InTable I theindicated inlettemperatures'. are. approximately the maximumtemperatures which. can be employed, they having been determined byraisingthe inlet'temperature gradually to. a point where the system,while still under. good-control, was nevertheless .cl'ose to gincipienttemperature run-away. Thus, the indicated conversions and otherylieldfactors given in the tablerepresent a practical maximum .for thecatalyst under study in eachrun.

Referencetothedata-presented in the foregoing table shows that.thosecatalysts provided with less than 0.5%

8 EXAMPLE 2 Theruns presented in Table II below were made under the sameconditions, and with the same equipment-as those of Example 1. Thisexample illustrates the effect of initial surface area, and shows thatcatalysts having surface areas above about 8t) m. g. have much lowermaximum permissible inlet temperatures than thoseof lower surface area.The difference becomes even more striking with those catalysts havingsurfaces areas of approximately 100 na /13., or..more.

Table II Catalyst Type Precipitated Alumina Gel Run N o 2706 2717 27212737 Composition, Wt. Percent:

K O- 0.10 0.10 0. 10 0.16 0.16 0.24 0. 24 0. 24 CriO, 21.19 21. 1921.19. 16. 6 1G. 6 13. 51 18.51 18.51 Surface Area, sq. Meter/Gram- 124S2 51 78 41 89 67 42 Max. Inlet Temp, F 1, 000. 1,100 1,135 1,105 1, 1301, 015 1, 120 1, 145 Product Analysis, Wt. Percent:

oke 1. 2. 3 2. 2. 7 2. 2.0 2.1 1. 9 1. 7 Hydrogen. 1. 8 2. 5 1.0 2. 3 3.0 1. 9 2. 5 1. 4 Cf Plus 0 3. 3 4. 5 5.0 5. 4 5. 5 2. 9 4. 5 5. 2Butoo1ene 3.3 8.1 9. G 6. 6 8.9 5. 3 7. 8 9. 2 Butenes 23. 8 26.8 2. 8v27. 7. 20. 7 25. 1 26. 4 22. 4 Butane 65. 2. 56. 2 58. 9 55. 5 (30. 262. 6 56. 8 60. (l Butadiene Equivalent Yield. 10. 6 26. 5 25. 2 25. 623.1 22. 5 25.0 24. 6 Selectivity 59. 8 j 63. 4 6 1. 6 G0. 2 61. 1 (53.6 6'3. 9 64. 7 Total Conversion 41. 8 50.8 55. 4 57. 3 54. 9 45. 7 50. 053. 6

K 0 gave .hagh total conversions and had good selectivity EXAMPLE 3 evenafter sustained .heat treatment equivalent to over six months of plantusage. The Bayer-type catalyst had good operating characteristics whenfresh, but fell off in activity after only four hours treatment at 1 600F., equivalent to three months plant service. Poor results were obtainedwith .the gel-type catalyst which contained no K 0.

It is also obvious from the data that catalysts contain ing more than0.5% .K O. show a decided tendency towards instability as evidenced by.a.high -coke/dehydro genation ratiowhich necessitates the employmentoflow Table III illustrates the stability of the potassiumcontainingalumina gel type catalysts under severe heat treatment. These runs wereconducted under the same conditions, and with the same equipment, asdescribed in Example 1. It will be noted that gel-type catalyst hasbetter. selectivity (coupled with high conversion) after 8.3 monthsequivalent commercial service than fresh Bayer-type catalyst, and isalso better after 9.3 months service than the Bayer-type aluminacatalyst after 6.4 months service.

Table III Catalyst Type... Bayer Type Precipitated Gel Run No 2663 26752706 2809 2805 Composition, Wt. Percent:

K 0, 0 I 0 0.16 0.14 0.17 'CriOgii 18.6 18. 6 16. 57 15. 7 16. 6Accelerated Aging Treatment, Hrs Fresh 28. Fresh 52 60 Temperature, "Fl, 600 1, 600 1, 600 Months Equlv. Plant Service. 0 6. 4 0 8. 3 9. 3SurfacelArea, rnfi/g .4. 60 37 78. 1 42 32. 7 Max- Inlet Temp.,'F...1,100 1,140 1,105 1,140 1,150 Product Analysis, Wt. Percent:

Coke 1. 6 1.1 2. 5 1.9 2. 2 .2 1.4 2.3 1.4 1.1. P .5 6. 8 5. 4 5.9 5. 5.0 4. 4 6. 6 9.0 8. 8 2 11.5 27. 7 22. 6 14.1 Butane .0 74. 8 55. 5 57.2 60. 0

Butane. Conversion, Percent '17. O 23. 2 42. 5 40. 8 32. 0 ButeneConversion, Percent 15.8 11.7 14. 8 18. 2 17. 0

Total Conversion. Percentun, 62. 8 34. 9 57. 3 59.0 49. 6

Butadiene Equivalent Yield 29.4 12.3 25. 6 24. 5 18. 7 Selectirity 62.553. 0 60. 2 67. 0 59. 0 Coke/Dchydrogenatlon Ratio 3. 4 5. 4 6. 1 4. 76. 0

inlet temperatures to avoid temperature run-away. Thus, EXAMPLE 4 whilealkali metal contents as high as 3% are beneficial insome conversionoperations whereinthe present catays find tility.. his is n t.hecaseinwdic. diab tic.

operations for dehydrogenating butane and butenes to butadiene.

ous alkali metals to obtain the comparative activity thereof at a.fixedtemperature level, both as freshly pre- Butane Conversion, percent- '9pared and after a:syntl1etic aging treatment for four hours at 1600" F.,equivalent to three'months service in a commercial dehydrogenationplant. While the amounts of alkalimetals used in these runs exceeded 0.5it is believed. that the data presented are valid in a comparativesense, it being noted that these were isothermal runs wherethetemperature of the catalyst bed was closely controlled by externalmeans. The catalyst used for run No. 8-601 was prepared by impregnatingpelleted Bayer Process activated alumina with'an amount of chromic acidsufficient to supply the catalyst when dry with 17% by weight chromiumoxide, following which the catalyst was dried andthen calcined at 1150F. for five hours. The catalyst used for run No. 8-602 was the; same asthat employed in run No. 8-601 except that 2 weight percent of K wasadded by impregnation in addition to the 17% 01- 0 and the catalyst thencalcined at 1150 F. for five hours. The catalystof run No.- 8-421 was agel-type alumina base 'material (Filtrol No. 90 pelleted in the samefashion as the Bayer Process material and prepared in the same fashionas catalyst No. 8-601, except for a heat treatment at 1600 F. beforeimpregnation with chromic acid. The catalystsused for runs No. 8-491,8-603, 8-604, and 8-605 were prepared from the gel-type base materialthe same as that for No. 8-421 and with the same processing steps,except for the introduction of the indicated amounts of alkali metaloxide added by impregnation along with the chromic oxide. The'catalystsdescribed above were tested under the following feed and isothermalprocessing conditions: feed, 100% butane; feed rate, 1.2 v./v./hr.;average catalyst temperature, 1100 F. pressure, inches Hg absolute; timeon-stream, 15 minutes. The data obtained in these runs are presented inTable IV, following.

10 production of a highly inferior catalyst having a low'yield ofdehydrogenation products andpoor dehydrogenation selectivity. r

A comparison of the catalyst used in runs No. 8-491 and No. 8-421clearly shows the benefits gained by the addition of potassium oxide tothe gel-type aluminabased catalyst, for example, in lowering the amountof coke and C and C cracked products while increasing the yield ofdehydrogenated products and improving the dehydrogenating selectivity. IIn comparing the catalysts used for runs No. 8-491, No. 8-603, No. 8-604and .No. 8-605, it is seen that the addition of sodium oxide to thecatalyst (run- No.

8-603) results in the production of a catalyst having high cokingcharacteristics, a low yield of dehydrogenation products and poorselectivity as compared with the other alkali promoted catalysts,particularly catalyst No. 8-491 containing potassium oxide. The tableshows also the addition of sodium oxide results in a catalyst havingpoorer characteristics than the catalyst containing only the gel-typealumina and chromium oxide after the aging treatment. Theaddition oflithium oxide and rubidium oxide is seen to result in improved cokingcharacteristics and selectivity over the nonalkali promoted catalyst,especially when the catalyst is fresh, though the improvement is not asgreat as when potassium oxide is the additive employed.

EXAMPLE 5 alumina gel type, and containing 0.16% K 0 and 6.7% I

Cr O The catalyst indicated in the tables as fresh Table IV CatalystType Commercial Bayer Precipitated Gel Run No I s-eoz Composition:

' Alkali M Alkali Metal, Wt CraOs, Wt. percent fresh Temperature, FSurface Area, Square Meters v gram 63 31 Produ Butene Conversion TotalConversion Butadiene Equivalent Yield. Selectivity 0:0: or one moor-gnuAs seen from the foregoing table, the two Bayer Process alumina-basedcatalysts (runs No. 8-601 and No. 8-602) have much poorer thermalstability than gel-type aluminabased catalysts of the other runs. Thisis evidenced by the relatively large decline in total conversion anddehydrogenation selectivity which occurs after heat treatment for fourhours at 1600 -F. Further, the addition of potassium oxide to the BayerProcess base catalyst caused was calcined for 4 hours at 1400 F. afterchromic acid impregnation. It will be noted in Table V from the catalystareas after accelerated aging and by comparison with similar data inTable III, that with catalysts of relatively low chromia content, thereis little loss of surface area with age. Likewise, catalyst activity, asshown by conversions and yields, improved with aging. Table ,V furtherillustrates the deleterious elfect of surface areas particularly largelosses in stability and resulted in the 7 exceeding m. /=g.,as'evidenced by the decrease in an 0: end: NWOOOu-n 1 1maximumpermissible inlet temperature and the attendant decrease,inyields and conversions.

Table V Catalyst Type Precipitated-Gel Run No 2786 2789 2793Composition, Wt Percent' K2 0.16 16 0.16 0.16 0.16 0110;. 6. 7 6. 7 6.76. 7 6. 7 Addrd Heat Treatment, Hrs. at

-i00 F Fresh 6 20 46 66 Months Equiv, Plant Service.-- 0 3. 6 6. 2 7.89.3 Surface Area, mJ/g- 105. 8 98. 1 89.8 84. 82.0 Max. Inlet. Tcmp., F980 1, 065 1,075 Product Analysis, Wt Percent:

1. 5 0.8 2. 5 Not tested 1. 7 1. 2 1. 2 D0. 2. 8 5. 3 4. 9 D0. 4. 2 6.06. 6 Do. 24.6 26. 5 29.8 D0. 64. 9 59. 8 55. 0 Do.

ButaneConversion, Percent.-. 33.1 38. 2 43.0 Do. Butcne Conversion,Percent. 8. 5 11. 7 13. 2 Do.

Total Conversion, Perccnt 41. 6 40. 9 56. 2 Do.

Butadiene Equivalent Yield 21. 1 24. 2 27.0 Do. Selectivity 63. 7 63. 362. 8 Do.

EXAMPLE 6 Table VI deals with adiabatic runs conducted under conditionsgenerally similar to those of Example 1, illustrating the utility of.the alumina gel type catalysts for productionof isoprene fromisopentane. The feed contained 98% isope ntane and 2% norrnal'pentane.The yield and conversion definitions are completely analogous .to-thoseset forth for butane dehydrogenation herein In conducting thedehydrogenation reactions embraced by the present invention, it isdesirable that hydrogen and product hydrocarbons be present in the,reactionmix only at relatively low partial pressures. This isparticularly true when producing butadiene from, butane and isoprenefrom isopentane, where two successive dehydrogenation steps areinvolved, each involving an increase in. volume and partial pressurerelative to the'feed hydrocarbons. A

further reason arises from the fact that as the partial ressure ofthe.dehy r g n ted.m ter lsi creas poly.- merization of these olefins andundue formation of coke results. Low partial pressure may be securedeither by operating during the hydrocarbon feed portion of the cycleunder a partial vacuum, i.e., at reduced total pressure, or by use of adiluent gas such as nitrogen or methane which does not take part in thereaction. It is preferred, therefore, to operate either at totalpressures between about 5 and 20 inches Hg absolute; or, if dilutionwith inert gas is employed, at hydrogen partial pressures in thereaction mix of between 1.0 and 10.0 inches of Hg absolute.

The various percentages employed herein are on a weight basis, unlessotherwise indicated.

While the invention has been illustrated in terms of a catalyst havingthe shape of small pellets, other shapes may also be used, e.g.,granules, spheres or even fine particles of the type used in fluidoperations.

I claim:

1. A dehydrogenation catalyst for the catalytic dehydrogenation of moresaturated C hydrocarbons to butadiene, which comprises an aluminaprepared by precipitation from a solution of an aluminum salt byaddition of an alkaline precipitating agent and, supported on saidalumina, a total of from about 0.025 to 0.5% by weight of at least onewater-soluble oxide selected from the group consisting of potassium,lithium and rubidium oxides, and a total of from about 3 to 40% byweight of at least one oxide selected from the group consisting ofchromium and molybdenum oxides, said catalyst having a surface areabetween about 30 and m. g.

2. A dehydrogenation catalyst for the catalytic dehydrogenation ofmoresaturated C hydrocarbons to butadiene, which comprises an aluminaprepared by precipitation from a solution of an aluminum salt byaddition of an alkaline precipitating agent and, supported on saidalumina, from about 0.025% to 0.5% by weight of watersoluble potassiumoxide and from about 5 to 25% by weight of chromium oxide, said catalysthaving a surface area between about 30 and 100 m /g.

3. A method of catalyst preparation which comprises impregnating analumina of gel type origin, as prepared by precipitation from a solutionof an aluminum salt by addition of an alkaline precipitating agent, witha heat decomposable salt of potassium in an amount sufi'icient toprovide the finished catalyst with from about 0.025 to 0.5% by weightpotassium oxide, calcining the resulting impregnated aluminum attemperatures above 1400 F. to reduce the surface area of the calcinedproduct to between about 80 and rn. /g., impregnating the calcined,potassium oxide-alumina product with a solution of a heat decomposablecompound of chromium in an amount .suflicient to provide the finishedcatalyst with from about 5 to 25% by weight chromium oxide, andcalcining. the. chromium compoundcontaining product at temperaturesabove about .1400 F. to reduce the surface areaof the catalyst tobetweenabout 30 and 80 mt /g, the alkali metal oxide present, on thefinished catalyst being capable of being removed by leaching with hotwater. j

4. The method of claim 3 wherein the final calcining step brings thesurfacearea of the catalyst-into a range of from about 50 to 80 mP/g.

References Cited-in the file of this patent UNITED STATES PATENTS2,420,563 Reynolds... May 13, 1947 2,474,440 Smith June 18, 19492,754,345 Kirshenbaum July 10, 1956 2,768,961 Weck Oct. 30, 1956

1. A DEHYDROGENATION CATAYLST FOR THE CATALYTIC DEHYDROGENATION OF MORESATURATED C4 HYDROCARBONS TO BUTADIENE, WHICH COMPRISES AN ALUMINAPREPARED BY PRECIPITATION FROM A SOLUTION OF AN ALUMINUM SALT BYADDITION OF AN ALKALINE PRECIPITATING AGENT AND, SUPPORTED ON SAIDALUMINA, A TOTAL OF FROM ABOUT 0.025 TO 0.5% BY WEIGHT OF AT LEAST ONEWATER-SOLUBLE OXIDE SELECTED FROM THE GROUP CONSISTING OF POTASSIUM,LITHIUM AND RUBIDIUM OXIDES, AND A TOTAL OF FROM ABOUT 3 TO 40% BYWEIGHT OF AT LEAST ONE OXIDE SELECTED FROM THE GROUP CONSISTING OFCHROMIUM AND MOLYBDENUM OXIDES, SAID CATALYST HAVING A SURFACE AREABETWEEN ABOUT 30 AND 100M.2/G.